The present invention relates to the field of battery manufacturing. More particularly, the present invention relates to the field of lithium polymer battery manufacturing.
Lithium polymer batteries are commonly manufactured using processes that incorporate the use of both heat and pressure to laminate layers of anodes, cathodes, and separators into a cell construction. Lamination can be performed by either of two well-recognized methods. One of the methods is commonly referred to as flat plate manufacture, and is performed using the components shown in FIG. 1. Using the flat plate manufacturing process, a load is applied onto two heated plates 10, where the cell assembly materials 11 are sandwiched between the plates 10. The other of the two recognized methods is commonly referred to as roller lamination manufacture, and is shown in FIG. 2. Using the roller lamination process, two heated rotating rollers 12 apply pressure to the cell assembly materials 11 as the materials 11 are pinched together while passing through a set gap between the rollers 12.
The roller lamination process and the flat plate lamination process are limited in the types of battery cells that they are able to construct. Because the pressure is applied uniaxially in either process, only a flat cell construction can be formed thereby.
Furthermore, using the existing roller and flat plate machinery, cells are constructed one at a time and then stacked together to give the desired application specific capacity. For example, if forty-five cells are stacked together, which is the maximum-sized stack using current processes, then forty-five individual lamination steps are required to make one cell.
Another problem associated with current battery cell manufacturing technology is that when the pieces are manufactured individually, they qualitatively vary. Using flat plate and roller lamination it is almost impossible to maintain consistent pressure across the entire cell. Inconsistent pressure contributes to short cell life and to poor performance of the battery. Using a flat plate manufacturing process, it is very difficult to maintain perfect parallelism between the two plates, especially with large plates. Using roller lamination, the slightest out of roundness of either roller translates to uneven pressure on the cell.
There is therefore an existing need for a battery cell manufacturing process that allows for the simultaneous manufacture of a large number of cells and enables consistent quality among the cells and within the cell layers. There is also an existing need for a manufacturing process that can be adapted for production of cells having a shape other than the flat prismatic construction.
It is an object of the present invention to meet the above-described needs and others. Specifically, it is an object of the present invention to provide a battery, more specifically a battery cell, and a method for manufacturing such. The method includes the steps of providing battery cell components such as a cathode, an anode, a separator disposed between the anode and the cathode, a cathode grid, and an anode grid, and applying isostatic pressure to the battery cell components. The isostatic pressure is applied using a hot isostatic press (HIP).
The method should further include the step of heating the components of the battery cell at least prior to the step of applying isostatic pressure. preferably, heating is performed while pressure is being applied.
The components of the battery cell should also include a binder material that includes a polymer that softens when heated, thus allowing the components named above to laminate. The binder material includes polyvinylidene fluoride, polymethylmethacrylate, polyvinylidene fluoride copolymer, polyacrylonitrile, and/or polyvinylchloride.
In a HIP, it is important to remove air from the surroundings of the cell components prior to adding heat and pressure. Accordingly, the method includes the step of wrapping the cell components in a heat-sealable film. Before sealing the film, a vacuum removes air and any other gases from the inside of the film.
The battery cell can be a flat prismatic cell. However, because isostatic pressure is applied instead of uniaxial pressure, cells of any conceivable structure can be manufactured. For example, the anode and the cathode can be spirally wound to form the wound cell, or round cell construction, prior to being subjected to isostatic pressure. The battery cell produced using the lamination method of the present invention is most preferably a component of a lithium polymer battery.
Additional objects, advantages and novel features of the invention will be set forth in the description which follows or may be learned by those skilled in the art through reading these materials or practicing the invention. The objects and advantages of the invention may be achieved through the means recited in the attached claims.
To achieve these stated and other objects, the present invention may be embodied and described as